1. Field of the Invention
This invention relates to a flux used in brazing an aluminum material, i.e. aluminum or an aluminum alloy.
2. Description of the Prior Art
When an aluminum material is brazed, it has been usual to employ as a brazing alloy a eutectic alloy of aluminum and silicon having a melting point which is somewhat lower than that of the aluminum material. In order to bond the brazing alloy to the aluminum material satisfactorily, it is necessary to remove all contaminants, such as an oxide film, from the surface of the aluminum material. A flux is used for that purpose. There has recently come to be used a non-corrosive flux composed of a KF-AlF.sub.3 complex. This substance melts at the eutectic point of KF-AlF.sub.3 and exhibits an excellent flux action. It is, however, at a temperature of 560.degree. C. or above that this flux begins to melt. It is, therefore, necessary to use a brazing alloy having a melting point which is several tens of degrees higher than 560.degree. C., and employ a correspondingly high brazing temperature. When a torch is used as a source of heat for brazing, a high temperature is difficult to control. Therefore, the use of the KF-AlF.sub.3 flux requires a high degree of skill and experience.
Anothe drawback of this flux is that it is not very effective as a flux for brazing an aluminum material containing magnesium.